This study is concerned with the reaction mechanism of the Na/K-ATPase. Biochemical studies are proposed to characterize the Na, K, and MgATP sites of the enzyme in terms of number, affinity, thermodynamic properties, and interactions. The role of enzyme isomerization in both the control of activity and in effecting cation transport will be investigated. Analyses of successive steps in the reaction sequence will concentrate on correlating the binding and release of Na and K with the hydrolyses of ATP.